Pianists of extraordinary talent, such as Christina Petrowska,spend a large part of their early lives perfecting technique…Miss Petrowska,a Canadian with a phenomenal ability to play the most difficult music cleanly, gave a demonstration of her achievements at Carnegie Recital Hall. A product of the Juilliard School who studied with Karlheinz Stockhausen and Gyorgy Ligeti in Europe, Miss Petrowska built most of her program around fiercely difficult contemporary works. She has fingers that work like chrome-plated pistons, and her high-seated position let her bring pulverizing power to bear.